Process Equipment and Plant Design
In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be

More than that for fluid flow
Less than that for fluid flow
Same as that for fluid flow
D₂ - D₁ (D₁ and D₂ are I.D. of inner and outer pipes respectively)

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Process Equipment and Plant Design
When one of the fluids is highly corrosive and has fouling tendency, it should

Perferably flow outside the tube
Preferably flow inside the tube for its easier internal cleaning
Flow at a very slow velocity
Flow outside the tube, when the flow is counter-current and inside the tube when the flow is co-current

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Process Equipment and Plant Design
Pick out the wrong statement pertaining to the comparative evaluation of performance of the packed tower and the plate tower.

The total weight of a dry plate tower is usually much more than that of a dry packed tower designed for the same duty
Plate tower is preferred over packed tower, if the operation involves liquids containing dispersed solids
In operations involving large temperature changes. (e.g. distillation), plate towers are preferred over packed towers as the packing may be crushed due to large temperature changes
Plate tower is perferred, if interstage cooling is required to remove heats of reaction or solution

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